Channelize

class baseband.tasks.Channelize(ih, n, samples_per_frame=1, *, frequency=None, sideband=None)

Bases: TaskBase

Basic channelizer.

Divides input into blocks of n time samples, Fourier transforming each block. The output sample shape is (channel,) + ih.sample_shape.

Parameters:

ihtask or baseband stream reader

Input data stream, with time as the first axis.

nint

Number of input samples to channelize. For complex input, output will have n channels; for real input, it will have n // 2 + 1.

samples_per_frameint, optional

Number of complete output samples per frame (see Notes). Default: 1.

frequencyQuantity, optional

Frequencies for each channel in ih (channelized frequencies will be calculated). Default: taken from ih (if available).

sidebandarray, optional

Whether frequencies in ih are upper (+1) or lower (-1) sideband. Default: taken from ih (if available).

See also

baseband_tasks.fourier.fft_maker

to select the FFT package used.

Notes

Instances initialize an FFT that acts upon axis 1 of an input with shape:

(samples_per_frame, n) + ih.sample_shape

Setting samples_per_frame to a number larger than 1 results in the FFT performing channelization on multiple blocks per call. Depending on the backend used, this may speed up sequential channelization, though for tests using numpy.fft the performance improvement seems to be negligible.

Attributes Summary

closed
complex_data
dtype	Data type of the output.
meta
ndim	Number of dimensions of the output.
offset
sample_rate	Number of complete samples per second.
sample_shape	Shape of a complete sample.
samples_per_frame	Number of samples per frame of data.
shape	Shape of the output.
size	Number of component samples in the output.
start_time	Start time of the output.
stop_time	Time at the end of the output, just after the last sample.
time	Time of the sample pointer's current offset in the output.

Methods Summary

close()	Close task.
inverse(ih)	Create a Dechannelize instance that undoes this Channelization.
read([count, out])	Read a number of complete samples.
seek(offset[, whence])	Change the sample pointer position.
task(data)
tell([unit])	Current offset in the file.

Attributes Documentation

closed = False

complex_data

dtype

Data type of the output.

meta = None

ndim

Number of dimensions of the output.

offset = 0

sample_rate

Number of complete samples per second.

sample_shape

Shape of a complete sample.

samples_per_frame

Number of samples per frame of data.

For compatibility with file readers, to help indicate what a nominal chunk of data is.

shape

Shape of the output.

size

Number of component samples in the output.

start_time

Start time of the output.

See also time and stop_time.

stop_time

Time at the end of the output, just after the last sample.

See also start_time and time.

time

Time of the sample pointer’s current offset in the output.

See also start_time and stop_time.

Methods Documentation

close()

Close task.

Note that this does not explicitly close the underlying source; instead, it just deletes the reference to it.

inverse(ih)

Create a Dechannelize instance that undoes this Channelization.

Parameters:

ihtask or baseband stream reader

Input data stream to be dechannelized.

read(count=None, out=None)

Read a number of complete samples.

Parameters:

countint or None, optional

Number of complete samples to read. If None (default) or negative, the number of samples left. Ignored if out is given.

outNone or array, optional

Array to store the samples in. If given, count will be inferred from the first dimension; the remaining dimensions should equal sample_shape.

Returns:

outndarray of float or complex

The first dimension is sample-time, and the remaining ones are as given by sample_shape.

seek(offset, whence=0)

Change the sample pointer position.

This works like a normal filehandle seek, but the offset is in samples (or a relative or absolute time).

Parameters:

offsetint, Quantity, or Time

Offset to move to. Can be an (integer) number of samples, an offset in time units, or an absolute time. For the latter two, the pointer will be moved to the nearest integer sample.

whence{0, 1, 2, ‘start’, ‘current’, or ‘end’}, optional

Like regular seek, the offset is taken to be from the start if whence=0 (default), from the current position if 1, and from the end if 2. One can alternativey use ‘start’, ‘current’, or ‘end’ for 0, 1, or 2, respectively. Ignored if offset is a time.

task(data)

tell(unit=None)

Current offset in the file.

Parameters:

unitUnit or str, optional

Time unit the offset should be returned in. By default, no unit is used, i.e., an integer enumerating samples is returned. For the special string ‘time’, the absolute time is calculated.

Returns:

offsetint, Quantity, or Time

Offset in current file (or time at current position).